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Antimicrobial resistance (AMR) poses a well-documented growing public health challenge, with multidrug-resistant infections contributing to nearly 5 million global deaths. Such infections could cause as many as 10 million annual deaths by 2050 if not action is taken.
Historically, infections ranked as the leading cause of death before antibiotics led to longer average human lifespans. Sir Alexander Fleming’s discovery of penicillin in 1928 followed by the subsequent commercialization of it and other antibiotics beginning in the 1940s helped turn the tide. Bacteria, however, are adept at adaptation. Over time, random mutations and gene-sharing among microbes have resulted in strains that can evade standard treatments — given rise to the term “superbugs.” This bacterial heterogeneity means that even within a single infection, subpopulations can respond differently to the same drug.
The photodynamic inactivation angle
Texas A&M’s team tackled the twin problems of microbial heteroresistance and persistence through photodynamic inactivation (PDI). In PDI, a light-sensitive molecule — known as a photosensitizer — yields reactive oxygen species when illuminated. These reactive species, in turn, damage bacterial cells, causing them to die. The researchers used curcumin, the bright yellow compound in turmeric, not only because it is a natural and affordable photosensitizer but also because bacteria can ingest it as a food source. Once inside bacterial cells, curcumin becomes lethal under 450 nm light, disrupting metabolic processes and diminishing resistance levels.
When we have a mixed population of bacteria where some are resistant, we can use photodynamic inactivation to narrow the bacterial distribution, leaving behind strains that are more or less similar in their response to antibiotics. It’s much easier now to predict the precise antibiotic dose needed to remove the infection.
Led by Dr. Vanderlei Bagnato, professor in the Department of Biomedical Engineering at Texas A&M University and senior author on the study, and Dr. Vladislav Yakovlev, also a professor in the Department of Biomedical Engineering at Texas A&M, the research showed that multiple cycles of PDI with curcumin killed large swaths of drug-resistant Staphylococcus aureus. That is, after PDI, the minimum antibiotic concentrations required to wipe out these bacteria dropped significantly.
Because curcumin is economical and widely available, using it in combination with light could expand treatment options in the developing world. The technique could also bolster military medicine, preventing hard-to-treat infections in battlefield contexts.
Curcumin’s broader antibacterial potential has been recognized in previous research, yet its clinical use has often been constrained by challenges such as poor water solubility (less than 0.1 mg/mL in many reports) and rapid metabolism. These factors limit its bioavailability and effective concentration within the body’s water-based environments. In addition, under near-neutral pH conditions, curcumin can degrade quickly, potentially losing much of its antimicrobial activity before it exerts any therapeutic benefit. Researchers have addressed these drawbacks through advanced formulations like nano-encapsulation and liposomal delivery. In the Texas A&M study, the photodynamic strategy helped localize curcumin’s impact at the site of bacterial cells, circumventing some of the solubility and stability bottlenecks that have long impeded its broader use in medicine.
